This invention relates to a developer for developing electrostatic images in electrophotography and electrostatic recording process.
Dry developers used in electrophotography and similar processes are generally divided into a one-component developer using a toner having a colorant dispersed in a binder resin alone and a two-component developer using the toner in admixture with a carrier. When these developers are used in copying operation, the developers must satisfy many factors such as fluidity, anti-caking, fixation, charging ability and cleanability in order that they adapt to the process.
For the purposes of improving the fluidity, anti-caking, fixation and cleanability, and adjusting and stabilizing the charging ability, at least two types of inorganic fine particles of silica, titania, alumina, zinc oxide, etc. having a smaller particle size than the toner particles are often added as the external additive.
As the copying speed is accelerated in the recent years, the developer is required to have more fluidity, cleanability, and stable and uniform charging ability. To produce images of better quality, the toner has shifted to a small particle size one. As compared with conventional toners commonly used in the art, the small particle size toner is poor in powder flow and its charging ability is readily altered by additives such as external additive. Then, depending on the type and particle size of inorganic fine particles such as silica fine particles added to the toner, the small particle size toner does not necessarily promise satisfactory results with respect to fluidity, charging ability and cleanability. A choice of the inorganic fine particles added thereto is important. Commonly used silica fine particles, whose mean particle size of primary particles is as small as 10 to 20 nm, are highly cohesive to each other and poorly dispersible, failing to meet the requirements of fluidity and cleanability. Using spherical silica fine particles is effective in improving fluidity and increasing the charge quantity, but due to an excessive charge quantity, the electrostatic adhesive force of fine particles to the toner support becomes stronger, resulting in a lowering of development, a lower image density and density variations. The silica fine particles used sometimes contain impurities, which affect the charging ability of the developer.
In addition to the silica fine particles, fine particles of titania, alumina or zinc oxide are further added for the purpose of controlling the charge quantity. However, crystalline fine particles are poor in fluidity and dispersibility due to their non-spherical shape, resulting in images being fogged (background staining). An attempt to add inorganic fine particles of at least two types as external additives to the toner particles was made for improving fluidity and cleanability and stabilizing charging ability. Because of fineness, these inorganic fine particles are difficult to disperse and mix uniformly, and result in a mixture of varying concentration which inevitably entails partial segregation. Due to a local varying degree of mixing, charging ability and cleanability become non-uniform. As a consequence, the desired effects are not fully exerted.
An object of the invention is to provide an electrostatic image developer having improved fluidity and cleanability as well as a stable charging ability.
We have found that amorphous ternary complex oxide fine particles are obtained by simultaneously atomizing a siloxane and two organometallic compounds of different metals M1 and M2 exclusive of silicon in a flame for combustion; that the ternary complex oxide fine particles consist essentially of silica and two metal oxides, are substantially free of chlorine, have a particle size of 10 to 500 nm, and have a silica content A of 1 to 99% by weight, a M1 oxide content B of 1 to 90% by weight and a M2 oxide content C of 1 to 90% by weight, all based on the weight of oxides excluding carbon, A+B+C≈100; and that when the ternary complex oxide fine particles are added as inorganic fine particles to toner particles, there is obtained an electrostatic image developer which exhibits smooth flow, effective cleaning and uniform and stable charging performance.
Accordingly, the invention provides an electrostatic image developer comprising amorphous spherical ternary complex oxide fine particles obtained by simultaneously atomizing a siloxane (which refers to an organopolysiloxane, hereinafter) and two organometallic compounds of different metals M1 and M2 exclusive of silicon in a flame for combustion, the fine particles being substantially free of chlorine, having a particle size of 10 to 500 nm, and having a silica content A of 1 to 99% by weight, a M1 oxide content B of 1 to 90% by weight and a M2 oxide content C of 1 to 90% by weight, all based on the weight of oxides excluding carbon, provided that A+B+C is substantially 100% by weight.
In a preferred embodiment, the ternary complex oxide consists essentially of silica and oxides of metals M1 and M2 as second and third components, the oxides of metals M1 and M2 being selected from among titanium oxide, alumina, zinc oxide, iron oxide, tin oxide, indium oxide, vanadium oxide, magnesium oxide, manganese oxide, boron oxide, cerium oxide, copper oxide, and nickel oxide.
In a preferred embodiment, the two organometallic compounds are selected from among alkoxy compounds, acylate compounds, alkyl compounds and chelate compounds of metals M1 and M2.
The complex oxide fine particles are preferably hydrophobized fine particles having introduced at their surface, units represented by the following formula (1):
R1xR2yR3zSiO(4-x-y-z)/2xe2x80x83xe2x80x83(1)
wherein R1, R2 and R3 each are independently a substituted or unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms, x, y and z each are an integer of 0 to 3, x+y+z is from 1 to 3.